The invention concerns a steel annealing basket for holding mass-produced parts of aluminium for degreasing and soft annealing, with a base and side walls bordered by a frame projecting from this.
Annealing baskets of the type described above are used for example for degreasing and soft annealing of aluminium slugs for the production of extruded can and tube bodies and technical extrusions. Annealing baskets of conventional design consist of a frame within which are welded the base and side walls. When heating the annealing basket filled with slugs to an annealing temperature in the range from 350 to 500xc2x0 C., the lubricant film initially adhering to the surface of the slugs vaporises, so that the slugs lose their initial slip ability as the temperature increases. Due to the heat expansion of the slugs, a pressure directed towards the side walls builds up in the annealing basket and which, as a result of the great softening of the aluminium and the heat expansion, which is around three times greater in comparison with a steel basket, leads to material deformations, in particular on the edges of the punched slugs, which can lead to production problems and rejects in the subsequent processing of the slugs by extrusion moulding.
The invention is therefore based on the task of creating an annealing basket of the type stated initially with which the localised deformations occurring on the soft aluminium parts, due to the pressure build-up as a result of the heat expansion, can be avoided.
The problem is solved according to the invention in that at least one side wall is connected to the frame by way of at least one aluminium element which deforms plastically on heating to an annealing temperature under the pressure occurring in the annealing basket by the heat expansion of the aluminium parts against the side walls so that the side wall, under the expansion of the basket volume, is moved outwards by an extent in at least one area adjacent to the frame.
In the connection according to the invention between the frame and the side wall, the pressure, due to the plastic deformation of the element softening to the same extent as the aluminium parts, is reduced by the movement of the side wall.
In a first embodiment of the annealing basket according to the invention, brackets are attached at least on one side wall in an edge area opposite brackets which are attached to the frame, and these together form a holder space for insertion of the element. The element is preferably an aluminium profile or a plate with substantially rectangular cross-section.
The frame can also be formed as a U-shaped profile which is open at the base, and the element, formed as an aluminium profile with substantially rectangular cross-section, can be inserted into the U-shaped profile, and the side wall lies against the side of the aluminium profile in an edge area.
The annealing basket according to the invention can be used for degreasing or soft annealing of any sort of aluminium parts. A particularly preferred area of application is the degreasing and soft annealing of aluminium slugs for extrusion moulding of can and tube bodies and technical extrusions.